Preparation of cracked gases

ABSTRACT

A PROCESS IS PROVIDED FOR THE PREPARATION OF CRACKED GASES IN WHICH A CHARGE-STOCK, SELECTED FROM THE GROUP CONSISTING OF OLIGOMERS OF LOWER OLEFINS, HYDROGENATION PRODUCTS OF LOWER OLEFIN-OLIGOMERS, COPOLYMERS OF LOWER OLEFINS AND THEIR HYDROGENATION PRODUCTS AND MIXTURES THEREOF, IS SUBJECTED TO VAPOR PHASE CRACKING IN THE PRESENCE OF A REFORMING CATALYST.

United States Patent 3,627,512 PREPARATION OF CRACKED GASES Axel Klaus Commichau, Hamburg-Rissen, Germany, assignor to Mobil Oil Corporation, New York, N.Y. No Drawing. Filed Jan. 22, 1970, Ser. No. 5,113 Int. Cl. C01b 1/16, 2/14 U.S. Cl. 48211 14 Claims ABSTRACT OF THE DISCLOSURE A process is provided for the preparation of cracked gases in which a charge-stock, selected from the group consisting of oligomers of lower olefins, hydrogenation products of lower olefin-oligomers, copolymers of lower olefins and their hydrogenation products and mixtures thereof, is subjected to vapor phase cracking in the presence of a reforming catalyst.

nwqnam BACKGRDUND OF THE INVENTION (1) Field of the invention (2) Description of the prior art Processes are known, to those skilled in the art, in which gaseous hydrocarbons and/ or liquid hydrocarbons boiling up to about 350 C. are cracked by reaction with steam or a steam-air mixture in the presence of a catalyst at temperatures from about 500 C. to about 1100- C. and at pressures from about 1 to about 50 atmospheres, producing mainly carbon monoxide and hydrogen. Such processes are particularly employed in the commercial large-scale production of hydrogen and combustible heating gas.

Heretofore it has been proposed that chemical synthesis waste products containing hydrocarbons be employed for the production of fuel gases having high heating power. Low boiling liquid hydrocarbons, such as methane, ethane, propane, butane, pentane, octane and the like, either individually or in mixtures thereof, have also been employed in cracking operations to produce gases suitable as combustible heating gas. Furthermore processes are also known to those skilled in the art for the vapor phase cracking of hydrocarbons in the gasoline range into hydrogenous gases by reaction with steam and/or nickel catalysts of specific compositions. For such cracking process, straight-chain and branch-chain hydrocarbons having from 1 to 5 atoms, for example methane, ethane, propane, butane, pentane, ethylene, propene, butene, pentene, butadiene and pentadiene can be employed.

In almost all instances the above described reactions take place in fixed installations where certain factors such as weight of the installation, or space requirements are of slight or secondary importance. Should, however, installations be employed for such cracking reactions in which space requirements and Weight, for example, are as low as possible and/or in which throughput quantities, in proportion to the entire plant, are relatively large, very high demands with respect to cracking are made on the charge stock in respect to purity and uniformity in order to avoid undesirable side reactions or functional disturbances in these special plants.

For various reasons many plants require, for example, that the charging stock comprise solely liquid hydrocarbons with a vapor pressure which is as low as possible at normal temperature in order to prevent vaporization. At the same time they also require that these hydrocarbons vaporize completely at the lowest possible temperatures in order to ensure satisfactory vaporization.

Hydrocarbons employed in present-day commercial operations are almost exclusively petroleum distillation fractions or fractions obtained from petroleum hydrocarbons after further processing stages, for example, cracking or reforming. These hydrocarbons are in the form of a mixture of many chemical products, which are dilficult to separate and which also usually contain undesirable impurities. Thus, these products do not produce satisfactory results insofar as the aforementioned special plants are concerned, and therefore to a certain extent such plants can not be constructed because of the lack of suitable charging stocks.

In addition to the foregoing, most of the catalysts employed in present-day industry constitute an optimum relationship between effectiveness, catalyst life and cost. Even if catalysts were to be employed whose effectiveness and yield were extremely high and which had an extremely long life, it has been found that they would still necessi tate the use of a charging stock of extreme purity and uniformity. A small, compactly built low weight, non-stationary steam reforming plant, employing a specially selected catalyst is exemplary of such special installations. Such a plant, in which a conversion installation is usually incorporated, is employed for the preparation of hydrogen for fuel cells.

The sulfur content of the charge stock plays a very important part with respect to the contamination of the catalyst. Although the hydrocarbon mixtures which are now always employed are described as possessing a low sulfur content, they are often found to have a sulfur content of more than 10 p.p.m., and such content is far too great with respect to the use of highly selective catalysts or for those catalysts which are to remain active for relatively long periods. When hydrogen is being produced, the cracking process is almost always followed by a one-stage or multi-stage conversion during which the carbon monoxide present in the gas is converted into carbon dioxide. In a similar manner, the conversion catalysts can be substantially deactivated or completely contaminated by the sulfur content in the gas, thus accounting for the fact that the sulfur content must be as low as possible in the case of employing the aforementioned special plants.

It is also known to those skilled in the art that when hydrocarbons are cracked in the gasoline boiling range, the tendency for carbon black to form increases substantially in the presence of impurities containing sulfur. A further disadvantage of the liquid hydrocarbons employed at the present time, for the above purpose, resides in their wide boiling range. In order to be able to crack hydrocarbon mixtures which often possess very wide boiling ranges, a two-stage process has been suggested to obtain cracked gases by catalytic cracking of petroleum hydrocarbons having from 2 to 30 carbon atoms, conversion being carried out in the first stage at a temperature from about 350 C. to about 650 C. and in the second stage at a temperature from about 550 C. to about 950 C. This two-stage cracking operation has been made necessary since the catalysts that have proved efiicient in the cracking of gaseous saturated hydrocarbons, become inactive during the cracking of higher boiling hydrocarbons, for example those in the gasoline boiling range, as a result of heavy carbon precipitation. Thus, the lack of uniformity of the charging stock has therefore had to be offset by expensive technical changes in the process. In addition, more or less large quantities of aromatics are always present in the charging stock employed in processes which are presently used, not only do these aromatics contain a considerably lower percentage of the necessary hydrocarbon than the aliphatics, but also require different cracking conditions, with the result that in selectively operating plants they have the effect of impurities. Furthermore, the aromatics, in particular, very easily result in carbon black formation, which not only makes the catalysts ineffective but can also gradually clog parts of the plant. It is also to be noted that the alkines and diolefins contained in the charge stocks employed at the present time, can often bring about obstructions since they often polymerize during heating-up and cause undesirable deposits.

It has not been possible, heretofore, to obtain completely satisfactory results in any of the presently known processes since the charging stocks for these processes are neither pure nor sufiiciently uniform. For these reasons attempts have been made to employ methanol in processes for producing hydrogeneous cracked gases, since such charge stock is available in a very pure and uni-form state. However, the fact that methanol has a 50 percent oxygen content results in that only about onehalf of the weight of cracked gas obtained from pure hydrocarbons is produced.

SUMMARY OF THE INVENTION In accordance with the present invention, a process is provided for the preparation of cracked gases, which are substantially sulfur-free, by subjecting a charge stock, having a boiling point from about 50 C. to about 350 C. and selected from the group consisting of oligomers of lower olefins, hydrogenation products of lower olefinoligomers, and copolymers of lower olefins and their hydrogenation products and mixtures thereof, to vapor phase cracking in the presence of a reforming catalyst. Furthermore, it has been found that products obtained, in accordance with the process of the present invention, from pure raw materials by chemical synthesis and not by physical separation of treated or untreated petroleum fractions, are superior to present-day commercial products. They are also found to be less costly and more readily available. In addition to their negligible sulfur content, they exhibit other highly desirable characteristics by reason of their natural extraordinarily high hydrogen content, chemical purity and uniformity due to their chemically defined structure. Oligomers of propylene and isobutylene have been found to be especially suitable, for example trimethyl pentane which is produced industrially by hydrogenation of diisobutylene and which comprises 98 percent pure isooctane with a boiling interval of only 8 C.

In accordance with the present invention it has also been found that copolymers of lower olefins, particularly those with a low polymerization level, and their hydrogenation products, boiling within the aforementioned range of from about 50 C. to about 350 C. at normal pressure, are also highly suitable for the present process, either individually or in admixture with other substances. The extraordinary low sulfur content, the extremely low concentration of resin-forming diolefins, alkynes and aromatics and the relatively narrow boiling range, are of particular advantage with respect to such petrochemically produced hydrocarbons and of the compounds hereinbefore described.

In carrying out the preparation of the cracked gases of the present invention, the aforementioned charge stock is subjected to vapor phase cracking as hereinbefore indicated, in the presence of water and a reforming catalyst. Any catalyst normally employed in reforming operations is suitable, and particularly preferred are reforming catalysts comprising at least one metal of the metals of Group VI and Group VIII of the Periodic Table of the Elements, their oxides and sulfides, either generally or on a porous carrier, for example aluminum. More specific types of catalysts that may be employed in the aforementioned vapor phase cracking under reforming conditions, are catalysts comprising chromia-alumina, molybdena-alumina, platinum-alumina, cobalt molybdena on alumina, nickel-uranium or platinum-rhenium-alumina. These catalysts may also be employed in combination with various carriers, particularly of the porous type, as hcreinbefore indicated.

DESCRIPTION OF SPECIFIC EMBODIMENTS The following examples will serve to illustrate the novel process for the preparation of cracked gases of the present invention. It will be understood, of course, that it is not intended the invention be limited to the particular products obtained or to the operations or manipulations involved. Various modifications thereof can be employed and will be readily apparent to those skilled in the art.

Example l.A desulfurized gasoline having a boiling range of from about 48 C. to about 170 C. at normal temperature and originating from a gasoline gasification plant, was subjected to a cracking operation in a reformer containing a uranium-nickel catalyst. This catalyst comprised about 20 percent by weight of nickel oxide-nickel uranate mixture (about 96 percent by weight of Ni() and about 4 percent by weight of NiU O and about 100 percent by weight of a heat-resisting carrier material, viz, alpha-alumina. In essence, this resulted in the presence of about 2 grams of the aforementioned nickel oxide-nickel uranate mixture on about 10 grams of the carrier. After activation of the catalyst, the mixture applied to the alumina was present during the vapor reforming operation in an amount, by weight, of about 98 percent nickel and about 2 percent U0 During the reforming operation, the reformer was maintained at a temperature between about 600 C. and about 1100 C.

In contrast to the above described desulfurized gasoline fraction, dlisobutylene, a dimer of isobutylene consisting, in major proportion of 2,2,4 trimethyl pentenes, was converted with water. The charging quantities were 0.2 to 2 liters of mixture per hour and the hydrocarbon: water ratio Was set at a mole ratio of C:H O such as 118, 1:6, 1:4 and 1:2. By comparison, it was found that when the desulfurized gasoline was fed in at a reaction temperature of about 800 C. or lower, there resulted increased precipitation of tar-like components in the reformer Within a short time and that at a reforming temperature of about 700 C. the plant became clogged so quickly that no more measurements could be carried out. On the other hand, where diisobutylene was employed, there resulted no reduction in throughput efficiency resulting from deposits, even at low reaction temperatures.

Example 2.The aforementioned desulfurized gasoline of Example 1 was compared with 2,2,4 trimethyl pentane, the hydrogenation product of diisobutylene, under the conditions described in Example 1. When the gasoline was employed, it was only possible to attain efficient operation of the reformer with an excess amount of water which corresponded to at least a CzH O mole ratio of 1:4. With a smaller water content, the undesirable methane content in the reformer exhaust gas was found to rise over 4 percent. It was found, however, possible to put through the hydrogenated product, in accordance with the present invention, with a C:H O ratio of 1:2, with the other conditions remaining the same, and the methane remainder content remaining substantially under 1 percent.

It will be understood that although the present invention has been described with preferred embodiments, various modifications and adaptations thereof may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand.

I claim:

1. A process for the preparation of cracked gases which comprises subjecting a charge stock, having a boiling point from about 50 C. to about 350 C. and selected from the group consisting of oligomers of lower olefins, hydrogenation products of lower olefin-oligomers and copolymers of lower olefins and their hydrogenation products and mixtures thereof, to vapor phase cracking in the presence of a reforming catalyst.

2. A process in accordance with claim 1 wherein the charge stock comprises an oligorner of propylene.

3. A process in accordance with claim 1 wherein the charge stock comprises an oligorner of isobutylene.

4. A process in accordance with claim 1 wherein the charge stock comprises a hydrogenation product of propylene-oligomers.

5. A process in accordance with claim 1 wherein the charge stock comprises a hydrogenation product of isobutylene-oligomers.

6. A process in accordance with claim 1 wherein the charge stock comprises a copolymer of propylene and isobutylene.

7. A process in accordance with claim 1 wherein the charge stock comprises a copolymer of isobutylene and butene.

8. A process in accordance with claim 1 wherein the catalyst comprises at least one metal of the metals of Group VI and Group VII of the Periodic Table of the Elements, their oxides and sulfides.

9. A process in accordance with claim 1 wherein the catalyst comprises chromia-alumina.

10. A process in accordance with claim 1 wherein the catalyst comprises molybdena-alumina.

11. A process in accordance with claim 1 wherein the catalyst comprises platinum-alumina.

12. A process in accordance with claim 1 wherein the catalyst comprises cobalt molybdena on alumina.

13. A process in accordance with claim 1 wherein the catalyst comprises nickel-uranium.

14. A process in accordance with claim 1 wherein the catalyst comprises nickel-platinum rheniuIn-alumina.

References Cited UNITED STATES PATENTS 10/1963 Lockerbie et al. 48214 UX 1/1964 McMahon 48214 UX US. Cl. X.R.

i27 UNITED STATES PATENT QFFICE CETIFICATE OF CORECTION Patent No, 3, 7,5 Dated December 1A, 1971 Inventor) AXEL KLAUS COMMICHAU It is certified that error appears in the above-identified patent and that: said Letters Patent are hereby corrected as shown below:

W Column 6, line 1 'Group VII" should read Group VIII Signed and sealed this 20th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOITSCHALK Attesting Officer Commissioner of Patents 

